1. Data Collecting and Sampling Techniques Lecture (3) Lecturer : FATEN AL-HUSSAIN

2. Note: This PowerPoint is only a summary and your main source should be the book. Data collection Survey Observational and Experimental Telephone surveys Mailed questionnaire surveys Personal interview

3. Note: This PowerPoint is only a summary and your main source should be the book. Some Sampling Techniques Random sampling Systematic sampling Stratified sampling Cluster sampling To obtain samples that are unbiased,statisticians use four methods of sampling:

4. Note: This PowerPoint is only a summary and your main source should be the book. Summer Term 1- Random sampling A random sample is a sample in which all members of the population have an equal chance of being selected.  Random samples are selected by using chance methods or random numbers For example:

5. Note: This PowerPoint is only a summary and your main source should be the book. Summer Term Q: Select random sample of 15 subjects out of 85 subjects: A: 12, 27, 75, 62, 57, 13, 31, 06, 16, 49, 46, 71, 53, 41, 02

6. Note: This PowerPoint is only a summary and your main source should be the book. Summer Term 2- Systematic sampling is a sample obtained by selecting every k th member of the population where K is counting number.  Systematic samples are obtained by numbering each value in the population and then selecting the k th value. For example:

7. Note: This PowerPoint is only a summary and your main source should be the book. Summer Term Decide on Sample Size: n Divide Frame of N individuals into Groups of k Individuals: k=N/n Randomly Select One Individual from the 1st Group Select Every k th Individual Thereafter N = 64 n = 8 k =64/8= 8 First Group

8. Note: This PowerPoint is only a summary and your main source should be the book. Summer Term 3- Stratified sampling is a sample obtained by dividing the population into subgroups or strata according to some characteristic relevant to the study. Then subjects are selected from each subgroup. For example:

9. Note: This PowerPoint is only a summary and your main source should be the book. Summer Term Female male A researcher select a random sample from each gender to check their blood pressure

10. 4- Cluster sampling is obtained by dividing the population into sections or clusters and then selecting one or more clusters and using all members in the cluster(s) as the members of the sample. For example: Note: This PowerPoint is only a summary and your main source should be the book. Summer Term

11. Randomly selected 2 clusters Randomly selected 4 clusters Note: This PowerPoint is only a summary and your main source should be the book. Summer Term

12. 1) Random : random number generator. 2) Systematic :every k th subject. 3) Stratified :divide population into group called “strata”. 4) Cluster :use intact groups. Note: This PowerPoint is only a summary and your main source should be the book. Summer Term

14. Types of Studies,Uses and Misuses of statistics Lecture (4) Lecturer : FATEN AL-HUSSAIN

15. Observational Study Experimental Study Types of Studies The researcher merely observes what is happening or what has happened in the past and tries to draw conclusions based on these observations. For example:  people who sleep 8 hours report better health.  A researcher counts the number of people living in each house in specific a street. The researcher manipulates one of the variables and tries to determine how the manipulation influences other variables. For examples:  Patients were randomly assigned to two groups was given drug A and the other group was given drug B to determine if the drug has an effect on patient’s blood pressure.  An Instructor has Three Teaching method,he want to apply a best method by seeing students grades. Note: This PowerPoint is only a summary and your main source should be the book.

16.  In a true experimental study, the subjects should be assigned to groups randomly. If this is not possible and a researcher uses intact groups, then he is performing a quasi-experimental study.

17. Note: This PowerPoint is only a summary and your main source should be the book. Dependent Variable or Outcome Variable Any Experiment has 2 Variables Independent Variable or Explanatory Variable The independent variable in an experimental study is the one that is being manipulated by the researcher. is the resultant variable

18. Note: This PowerPoint is only a summary and your main source should be the book. Note :Statistical studies usually include one or more independent variables and one dependent variable. For example: exercise, diet ( independent ) Health (dependent) Independenttemperature of water exercise Dependenttime to cook an egg health Influence

19. A confounding variable: is the variable that influences the dependent or outcome variable but was not separated from the independent variable.( variable that influence with other variable) For example: cigarette health age cigarettehealth confounding variable Influence Note: This PowerPoint is only a summary and your main source should be the book.

20. For Example :subjects on exercise program may improve their diet and perhaps that improve their health in other ways not due to exercise alone. Then diet becomes confounding variable. exercise health diet exercise health confoundin g variable Influence

21. Note: This PowerPoint is only a summary and your main source should be the book. Control Group Types of group Treatment Group The group that received the special instruction. The group that dose not received the special instruction.

24. Note: This PowerPoint is only a summary and your main source should be the book. Uses and Misuses of statistics Suspect sample Ambiguous Averages changing Subject Detached Statistic Implied connection Faulty Survey Question Misleading Graphs

25. Note: This PowerPoint is only a summary and your main source should be the book. 1- Suspect sample: small samples,convenience sample, volunteer sample For example: if 4 doctors were surveyed from 100 doctors. 2- Ambiguous Averages: measures that are loosely called averages are the mean, median, mode and midrange. People who know this can without lying, select one of them to support their position.

26. Note: This PowerPoint is only a summary and your main source should be the book. 3- changing Subject : can occur when different values are used to represent the same data. For example: if one political candidate say “ I will increase salaries a mere 3%” And another one say “I will increase salaries a whopping 6,000,000 $” And 3% =6,000,000

27. Note: This PowerPoint is only a summary and your main source should be the book. 4- Detached Statistic: it is the one in which no comparison is made.(Compared to what?) For example, one may say that “Our cookies has one-third fewer calories” Here, fewer than what? 5- Implied connection : Usage of words such as may, suggest or some that imply connections but there is no guarantee For example: Eating fish may help to reduce your cholesterol.

28. 6-Misleading Graphs: if graphs are drawn inappropriately, they can misrepresent the data and lead to false conclusions. 7- Faulty Survey Question : should be sure that the questions are properly written since the way questions are phrased can influence the way people answer them. Note: This PowerPoint is only a summary and your main source should be the book.

29. Chapter Definitions Note: This PowerPoint is only a summary and your main source should be the book.